1. Field of the Invention
This invention relates in general to methods and apparatus for manipulating material such as concrete, sand, gravel, or other loose material. In particular, the invention relates to apparatus for screeding and trowelling concrete to a smooth, level surface.
2. Description of the Prior Art
When concrete is poured, the concrete must be leveled and smoothed (screeded) before the concrete sets. A screeding machine is often used to level the concrete, especially when a large area of concrete is to be poured. Such machines are generally required to move along heavy, cumbersome rails or guides. A trowelling machine may then be used to smooth the surface of the concrete.
U.S. Pat. No. 4,655,633, issued Apr. 7, 1987, to Somero et al., discloses a screeding apparatus having a cantilevered boom mounted on a frame. A screed is mounted on the boom for movement along the boom. The elevation of the screed is automatically adjusted relative to a laser beacon reference plane. The boom can be rotated about a vertical axis and can be extended and retracted.
U.S. Pat. No. 4,371,287, issued Feb. 1, 1983, to Johansson, discloses a trowelling device. The Johansson device includes a cantilever arm on a carrier. A trowel is carried in a pedestal structure located at the distal end of the arm. The vertical position of the trowel can be adjusted to a selected position relative to a horizontal laser beam.
When a large concrete floor is poured, there may be obstructions in the floor, such as plumbing pipes or vertical columns. These obstructions may not allow a screeding or trowelling device to move straight across the floor. In such cases, it is desirable for the screed or trowel to be very maneuverable. In particular, it is helpful if the head can be rotated about a vertical axis as the head is pulled or pushed across the floor. Such rotation, combined with the other movements of the current machine, would create maneuverability which not only would allow the apparatus to be effective in a wider range of applications, but also would permit concrete to be moved over large distances in any direction.
Despite the prior art just mentioned, screeding concrete by manually passing the edge of two by four planks across the surface of the concrete is still prevalent today when pouring floors of buildings or parking lots. This is because prior art machines are either too large and immobile (slip-form pavers) or require large guides or rail supported screeds. Such guided screeds are cumbersome and labor intensive to set-up and usually require slabs to be poured in strips between the guides. Strip pouring is time consuming because a subsequent strip can not be poured until the previous one has set. However, manually screeding with two by four planks is also labor intensive and is not as precise as machines.